Method and device for the continuous production of steel using metal charge material

ABSTRACT

A method for the continuous production of steel using metal charge material that is preheated in an upper part of a melting vessel, is then melted in a lower part of the melting vessel with fossil fuels and the molten material is continuously discharged into a treatment vessel in which the desired steel quality is adjusted while gases are introduced into the melting vessel from the exterior to afterburn the melting exhaust gases. The process gases are step-wise afterburned when ascending in the melting vessel by introducing the afterburn gases into the interior of the charge material column by way of an interior shaft that projects into the material column and in whose walls inlet openings for the gases are disposed and form afterburn planes arranged one on top of the other.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Divisional application of U.S. patentapplication Ser. No. 10/498,632, filed Mar. 17, 2005, now U.S. Pat. No.7,897,100, which is a 371 of International application PCT/EP03/00123filed Jan. 9, 2003, which claims priority of DE 102 05 660.9, filed Feb.12, 2002, the priority of these applications is hereby claimed and theseapplications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a process for the continuous production of steelwith the use of metal charge materials, such as scrap, sponge iron, orthe like, wherein the charge materials are preheated in an upper part ofa melting vessel and then melted in a lower part of the melting vesselusing fossil fuels, wherein the molten metal is continuously dischargedinto a treatment vessel, in which the desired grade of steel isadjusted, and wherein gases are introduced into the melting vessel fromthe outside for post combustion of the process gases.

2. Description of the Related Art

The invention also concerns equipment for the continuous production ofsteel with the use of metal charge materials, which comprises a meltingvessel with at least one fossil fuel burner that acts on the metalcharge materials in a lower part of the melting vessel, and a treatmentvessel, which is connected with the lower part of the melting vessel bya taphole, such that the molten metal is continuously discharged intothe treatment vessel, in which the desired grade of steel is adjusted,such that the charge materials are preheated in an upper part of themelting vessel by the process gases, and such that gases are introducedinto the melting vessel from the outside for post combustion of theprocess gases. In the treatment vessel, the molten iron is subjectedespecially to superheating and an alloying treatment to produce steel.

A method of this type and equipment of this type are described in DT 2325 593. A method is described for the continuous production of steelwith the use of charge materials, such as scrap, sponge iron, or thelike, which are continuously melted from below by a burner lance in ashaft furnace, which serves as the melting vessel, wherein the moltenmetal is discharged into a heated continuous vessel, in which slagseparation is carried out continuously, and wherein the material presentin the vessel is superheated, and the desired steel analysis is adjustedby the addition of suitable alloying additives and deoxidationadditives. The superheating and slag reduction are accomplishedelectrically. The continuous vessel is heated for this purpose byinduction or by an electric arc. A lance-like oil/oxygen burner isinserted in the shaft furnace by means of a lance guide in such a waythat it can be moved vertically into the interior of the melting vessel,and the flame produced by the burner acts on the charge material frombelow and continuously melts it. Air for post-combustion of the exhaustgases from the melting process, which are used to preheat the materialto be melted, can be introduced through an annular gap in the casing ofthe shaft furnace. The interior of the melting vessel is essentiallycylindrical and can have a diameter that increases slightly towards thebottom.

This continuous process of melting scrap by the countercurrent principleis also described in Stahl und Eisen, 92 (1972), No. 11, p. 501. In thismode of operation, a column of scrap is melted from below with anoil/oxygen burner. The molten metal runs continuously out of the meltingvessel together with the iron oxide slag that forms. At the same time,the column of scrap is replenished by continuous recharging. A problemassociated with this process is that, although the sensible heat isused, the share of chemically bound exhaust gas heat remains unutilizedfor preheating. Moreover, the process has the problem of high ironoxidation due to the use of fossil fuels in combination with oxygen.

A different direction of development is described in Stahl und Eisen 115(1995), No. 5, p. 75. In this case, scrap is preheated in a preheatingcolumn and melted down in an iron bath reactor. Either the preheatingcan occur in the iron bath reactor itself before the melting, or thescrap is preheated in a basket located above the melting reactor andthen allowed to fall into the reactor. During the melting, coal andoxygen are blown into the iron bath, and the exhaust gases can bepost-combusted above the melt in the reactor. To minimize oxidation ofthe scrap during the preheating, the fuel gas is burned in stages duringthe preheating.

SUMMARY OF THE INVENTION

The objective of the present invention is to optimize a process of thisgeneral type and equipment of this general type with the introduction ofmelting energy by fossil fuels and with utilization of the chemicalexhaust gas heat to preheat the charging material.

In accordance with the process of the invention, as the process gasesascend in the melting vessel, they are post-combusted in stages inpost-combustion planes (E1-E4) arranged one above the other, such that,to accomplish this, in addition to the post-combustion gases introducedinto the column of charge materials from the outside, post-combustiongases, i.e., oxidizers, such as oxygen, air, or a mixture thereof, arealso introduced or injected into the interior of the column of chargematerials through an interior shaft that projects into the column ofcharge material.

Optimum post combustion with a low level of oxidation of the chargematerial and thus a high degree of efficiency of the utilization of thechemical heat of the exhaust gases are achieved by the combination ofpost combustion in stages and the introduction of post-combustion gasesinto the column of charge materials both from the outside and from theinside. Due to the interior shaft, fossil energy can be effectivelyintroduced into the column of charge material, so that favorable heattransfer and lower iron oxidation are achieved. The post-combustion gasmust move only short distances to achieve mixing and thus postcombustion of the process gases.

Advantageously, the amount, type, and/or composition of thepost-combustion gases is adjusted as a function of the properties of theprocess gases along the height of the melting vessel, preferably in eachpost-combustion plane or in most of the post-combustion planes, and as afunction of the desired degrees of post combustion at a certain height,for example, by suitable metering of mixtures of air and oxygen. It isalso proposed that the post combustion be influenced by, among othermeans, adjustment of the amount, type, and/or composition of theoxidizers and fossil fuels and by the position of the burner in relationto the interior shaft.

In particular, it is proposed that the post-combustion planes beadjusted in height by varying the arrangement of the interior shaftrelative to the melting vessel and/or that they be adjusted by rotationof the interior shaft about its longitudinal axis. In this way, thepost-combustion planes, which are formed by the admission ofpost-combustion gases from the outside and the inside, can be variablyadjusted relative to one another. In accordance with an especiallypreferred refinement of the invention, at least a portion of the processgases to be post-combusted is removed from the column of chargematerials, and these process gases are post-combusted outside the columnof charge materials, especially outside the melting vessel. Thepost-combusted process gases are then returned to the column of chargematerials in a plane above the plane from which they were removed.

The post combustion occurs in corresponding combustion spaces, which areseparate from the column of material and into which the post-combustiongases are introduced. To this end, feed lines for the post-combustiongases open into the combustion spaces, and the post-combustion gas comesinto contact with the process gases circulating through the combustiongases. Introduction of the post-combustion gases with an injector effectis especially advantageous due to an entrainment effect.

With respect to the equipment of the invention, the melting vessel has acentrally arranged hollow interior shaft, which extends into the meltingvessel from above along the longitudinal axis of the melting vessel.This results in the formation of an annular shaft furnace. The wall ofthe interior shaft has inlets for post-combustion gases, which arearranged one above the other along the casing of the interior shaft andform the post-combustion planes that are arranged one above the other.The inlets are connected especially with separate feed gas lines. Thismakes it possible to introduce the post-combustion gases or oxidizersinto the scrap column containing the charge material from the insideaccording to the desired post-combustion distribution.

Preferably, measuring instruments are provided for determining theproperties of the process gases along the given height of the meltingvessel, preferably in each post-combustion plane or in selectedpost-combustion planes, and means are provided for making correspondingadjustments of the type, amount, and/or composition of the gases beingadmitted for the post combustion.

It is proposed that the inlets arranged in a given plane in the meltingvessel have a staggered arrangement in relation to two planes of inletsof the interior shaft that are arranged one below the other, i.e.,post-combustion planes arranged one above the other are alternatelyformed by the interior shaft inlets and the inlets in the vessel wall,which can be varied by adjusting the interior shaft relative to themelting vessel. This makes it possible to adjust not only the type,amount, and composition of the post-combustion gases, but also thepost-combustion planes.

In accordance with an especially preferred embodiment, not only theprocess gases formed during the melting are post-combusted to utilizethe chemical energy, but also the process gases formed during thetreatment of the molten metal in the treatment vessel. For this purpose,the gas spaces of the two vessels are connected with each other in agastight manner.

Energy is supplied primarily by fossil fuels in combination withoxidizers, for example, a natural gas/oxygen mixture or oil/oxygenmixture without conversion to an electric form. In this regard, thetreatment vessel should also be operated at least partly by means offossil energy, while the remaining energy is supplied in the form ofelectric energy.

To achieve further reduction of undesired oxidation of the iron-bearingcharge materials during a post combustion, at least part of the postcombustion of the gases, preferably a large part, should be carried outin a place that is spatially separated from the column of chargematerial, specifically, in the post-combustion spaces or channels, whichare integrated in the wall of the melting vessel or outside the meltingvessel and/or in the interior shaft, and into which the feed lines forpost-combustion gases open, and in which the gas emerging from theinlets, which supports the post combustion, comes into contact with theexhaust gases circulating in the channel. Preferably, these channels canalso be provided in the region in which the inlets open in the wall ofthe interior shaft. Post combustion of the exhaust gases in thecombustion spaces that are separated from the scrap column has theadditional advantage that the scrap is not overheated. In accordancewith an especially preferred embodiment, a combustion space extendsannularly around the melting vessel. Alternatively, it is possible toprovide several independent spaces, which are arranged especially sideby side at the same height. In accordance with another embodiment, thecombustion spaces are formed as lines, into which the process gas on a(lower) plane is drawn in, and which convey the post-combusted processgas back into the shaft on a plane situated at a higher level. Thesuction effect is based on the fact that the flow resistance for theprocess gases through the column of material is higher than the flowresistance through the lines.

Additional details and advantages of the invention are apparent from thedependent claims and from the following description, in which theembodiments of the invention illustrated in the drawings are explainedin detail. In this connection, besides the combinations of featuresspecified above, features alone or in other combinations are an integralpart of the invention.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing:

FIG. 1 shows a partial sectional side view of equipment in accordancewith the invention for producing steel with a melting vessel and atreatment vessel.

FIG. 2 shows a partial section of FIG. 1 showing the measurement andcontrol engineering for carrying out the post combustion in stages.

FIG. 3 shows a cross section through the melting vessel with an interiorshaft.

FIG. 4 shows a sectional view of a preferred embodiment of the meltingvessel with an annular combustion space.

FIG. 5 shows a detail view of FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows equipment 1 for the continuous production of steel with theuse of metal charge materials, especially scrap. It consists of amelting vessel 2 and a superheating and treatment vessel 3 installednext to it, i.e., a furnace in which superheating of the melt producedin the melting vessel 2 and alloying adjustments of the steel arecarried out. The melting vessel 3 comprises a shaft 4, into which aninterior shaft 5 extends gastight from above, not quite to the lowerpart 6, here the base, of the shaft 4 and substantially up to a level ofa taphole 10. An annular shaft furnace is formed in this way.Hereinafter, the melting vessel 3 will be referred to as the shaftfurnace. In the embodiment shown in the drawing, the vessel wall 7 ofthe shaft furnace has the shape of a cone whose diameter increasestowards the bottom, while the interior shaft 5 has the shape of a conewith decreasing diameter towards the bottom. As a result of thisexpanding structure of the shaft furnace, the scrap column 8, which ischarged from above, is more mobile from top to bottom, and the freespace that forms towards the bottom allows sufficient scrap to advancefrom top to bottom. In the meltdown zone 9, i.e., in the lower third ofthe shaft furnace, the shaft furnace can become cylindrical or can evenbe designed with the opposite conical shape, i.e., with decreasingdiameter towards the bottom. The opposite conical shape of the interiorshaft 5 increases this free space towards the bottom; however, theinterior shaft may also be cylindrically shaped.

The shaft furnace is connected with the treatment vessel 3 via a taphole10 arranged in the lower part and a refractory seal. In the embodimentshown here, the treatment vessel 3 consists essentially of a lowermolten bath vessel part 11 and an upper vessel part 12. The process iscarried out by charging scrap 8 into the shaft furnace from above. Thescrap column is preheated by the hot exhaust gases 13 from the treatmentvessel 3 and the shaft furnace, which flow in the opposite directionfrom the scrap, and is melted down in the lower part 9 of the shaftfurnace by a burner 14, which is integrated in the tip 15 of theinterior shaft 5. The molten metal 16 flows continuously into the lowermolten bath vessel part 11 of the treatment vessel 3 through the taphole10. In the opposite direction, exhaust gases from the treatment vessel 3can flow through the taphole 10 or through a separate gas line into themelting vessel.

The interior shaft 5, which extends centrally into the scrap column 8,has feed lines 18, 19 in its hollow interior space 17 and inlets 21 inits wall 20 for systematically conveying post-combustion gases oroxidizers 22 brought in through the feed lines 18 from the interiorshaft 5 to the scrap column 8. The inlets 21 are located in planes E1,E2 arranged one above the other. They are arranged radially in the wall20 of the interior shaft 5 and transversely with respect to thelongitudinal axis of the interior shaft. In this way, they formpost-combustion planes E1, E2, which can expand into sectors as a resultof the flow of the exhaust gas. It is also possible for several inletsto be arranged directly one above the other to form a sector. The hotexhaust gases 13 flowing through the scrap 8 are post-combustedaccording to the given post-combustion plane E1, E2 and according to themixture of post-combustion gases 22 adjusted for the givenpost-combustion plane.

In addition, the tip 15 of the interior shaft 5 facing the bottom 6 ofthe shaft furnace 4 has a burner 14, which is supplied with fossil fuels23 by a separate feed line 19. The fossil energy sources 23 arepreferably gas/oil, which, together with oxidizers (for example, oxygen,air, or mixtures thereof) introduced through a separate line, are mixedand burned in the burner. The combustion of the fossil fuels to melt thescrap 8 is preferably carried out with less than the stoichiometricamount of oxygen, so that less oxygen is available for oxidation of theiron.

By feeding the gases 22 that support the post combustion and the fuels23 necessary for melting the scrap through the interior shaft 5, theyare already preheated. To increase the degree of preheating, aheat-exchange unit 24 may be installed outside the interior shaft 5. Thegases and fuels 22, 23 are then heated by countercurrent heat exchangewith hot exhaust gases 13.

After preheating and melting of the scrap 8, the melt 16 is continuouslydischarged into the treatment vessel 3. The treatment vessel 3 isrotatably supported. After the steel treatment has been completed, thevessel is rotated about an axis of rotation 26 that is parallel to thehorizontal foundation 25 to tap first the slag and then the molten steelthrough a taphole 27 in the lower part 11 of the vessel. To this end,the lower part 11 of the vessel is supported in a swivel mechanism 28.It can be moved up to the melting vessel 2 by means of a movable bottomplate 25. In the illustrated embodiment, the treatment vessel 3 isdesigned as an arc furnace with two electrodes 29, 30, which arepositioned in the furnace by a holding device 31. However, the power mayalso be supplied with three-phase current through three electrodes. Theenergy necessary for treatment of the melt can also be introduced byfossil fuels. The treatment vessel 3 is closed by an upper vessel part12 or a cover. A lance 32 for supplying carbon sources and/or oxygen orair is provided in the cover for carrying out the superheating and slagfoaming. In addition, the vessel 3 has a charging device 34 forsupplying additives for the metallurgical treatment of the melt.

The positioning of the post-combustion planes E1, E2 in relation to themelting vessel and thus in relation to the post-combustion planes E2, E4and the properties of the emerging gases 22 are controlled orautomatically regulated in the given post-combustion planes as afunction of the properties of the process gases along the height of themelting vessel. This is shown in FIG. 2. In each post-combustion planeor in selected post-combustion planes, means 35 are provided fordetermining the given process gas properties at a given height of themelting vessel. These means 35 take and further convey gas samples ordetermine the composition and measure the temperature of the hot processgases. The process gas samples taken in the post-combustion planes canbe analyzed in an analyzer 36 a. Depending on these results, which aretransmitted to a computer unit 37 over instrument leads 36, theproperties of the gases 22 for the post combustion are calculated, andsuitable adjustment means 39 are activated over control lines 38. Theseadjustment means 39 comprise, for example, metering and mixing devicesfor air and oxygen, i.e., a distributor of the oxidizing agents for theindividual post-combustion planes. The post combustion is controlled notonly by adjustment of the parameters of the gases 22, but also byvariation of the arrangement of the interior shaft 5 relative to theshaft furnace or by variation of the position of the burner 14 in theinterior shaft 5. The interior shaft 5 can be moved along thelongitudinal axis of the shaft furnace by positioning mechanisms or apositioning device 40. In addition, turning mechanisms 41 may beprovided, which allow the interior shaft 5 to be rotated about itslongitudinal axis. The interior shaft 5 preferably can be rotated up toan angle of at least 0.5φ relative to the shaft furnace (see FIG. 3) toallow favorable positioning of the inlets 21 in the interior shaft 5 inrelation to the inlets 42 in the vessel wall 7 of the outer shaft. Theinlets 42 are further discussed below. Each of the one or more burners14 can be moved within the interior shaft 5 by positioning mechanisms43.

At the same time, measuring devices 44 for determining the position ofthe interior shaft 5 in relation to the shaft furnace and measuringdevices 45 for determining the position of the burner 14 in the interiorshaft 5 are provided. These measurement results are also transmitted tothe computer unit 37 and are used to control or automatically regulatethe properties of the gases 22, 23 for the post combustion viaappropriate actuation of the positioning and turning mechanisms 40, 41,43. This preferably occurs in such a way that local overheating of thesurface of the scrap to greater than 90% of the melting point of ironoxide is not reached in any post-combustion plane or post-combustionsector, and that the degree of post combustion of the exhaust gasemerging from the melting vessel is approximately 100%.

In addition to the inlets 21 in the interior shaft 5, inlets 42 arearranged in the wall 7 of the melting vessel 4 and are connected to feedlines for post-combustion gases 22. In this regard, the planes E1, E2and E3, E4 formed by the interior shaft inlets 21 and the vessel wallinlets 42, respectively, are offset relative to each other, so that apost-combustion plane with inlets 42 from the outside of the vessel anda post-combustion plane with inlets 21 from the inside of the interiorshaft 5 alternate from bottom to top. The amount by which they areoffset is up to 50% of the distance between the planes of the inlets.This offset arrangement prevents it from becoming too hot in individualplaces in the scrap column 8, while other regions remain too cold, sothat post combustion does not occur. The external and internal injectionports or slots are arranged in such a way that the inlets do notinterfere with one another, but rather create favorable gas distributionin the scrap column by their arrangement relative to one another. Inaddition, FIG. 3 illustrates a preferred configuration of the angle ofthe inlets 21, 42 relative to each other. The inlets 42 in the wall 7 ofthe melting vessel 2 are arranged at an angular displacement of up to0.5φ, preferably at an angular displacement of 0.5φ, relative to theinlets 21 in the interior shaft 5, where φ is the angle between twoadjacent inlets 42 in a post-combustion plane.

In accordance with an especially preferred embodiment, which isillustrated in FIGS. 4 and 5, the wall 107 of the shaft furnace isprovided with an annular channel or combustion space 146 at the heightof the inlets 142.

In the design shown here, this combustion space 146 consists of a bulge147 in the vessel wall 107, such that the interior of the combustionspace 146 is separated from the interior of the shaft furnace and thusfrom the scrap column 8 by a partition 149 that is formed as acontinuation of the inside surface 148 of the vessel wall 7. Thispartition 149 is positioned at the combustion space 146 in such a waythat an inlet zone 150 for process gases 113 flowing past it is formedat the bottom, and an outlet zone 151 for post-combusted gases 113′ isformed at the top. This allows the process gases 113 to circulatethrough the combustion space or channel 146 and the post combustion tooccur to a large extent in the combustion space or channel 146. FIG. 5shows the arrangement of the inlets 142 in the vessel wall 107 of theshaft furnace in relation to the partition 149. The angle α formed bythe opening of the inlet ports 142 or slots between the linear extensionof the opening and the partition 149 can take on values between 90° and−90°. The opening angle is preferably determined in such a way that anentrainment effect is produced for the process gas flowing in. The inlet142 can also be designed as a de Laval nozzle, i.e., a nozzle that firstconverges and then diverges to produce acceleration of the gases.

All together, the proposed process and equipment offer an effectivepossibility for steel production with the use of fossil energy and aretherefore also of interest for use in sites with poor electric energysupply.

1. A process for continuous production of steel using metal chargematerials, comprising the steps of: preheating the charge materials inan upper part of a melting vessel and then melting the charge materialsin a lower part of the melting vessel with fossil fuels; continuouslydischarging the molten metal into a treatment vessel, in which a desiredgrade of steel is adjusted; introducing gases into the melting vesselfrom outside for post combustion of process gases, wherein, as theprocess gases ascend in the melting vessel, the process gases arepost-combusted in stages in post-combustion planes arranged above oneanother; and, to accomplish this, also introducing post-combustion gasesinto an interior of a column of charge materials through an interiorshaft that projects into the column of charge material through inlets ina wall of the interior shaft.
 2. The process in accordance with claim 1,including adjusting an amount, type, and/or composition of thepost-combustion gases as a function of properties of the process gasesalong a height of the melting vessel, the properties includingcomposition and temperature of the process gases.
 3. The process inaccordance with claim 1, including adjusting an amount, type, and/orcomposition of the fossil fuels and a position of at least one burner,which is movably installed in the interior shaft, as a function ofproperties of the process gases along a height of the melting vessel,the properties including composition and temperature of the processgases.
 4. The process in accordance with claim 1, including adjustingthe post-combustion planes by varying an arrangement of the interiorshaft relative to the melting vessel with respect to height and/or byrotating the interior shaft about a longitudinal axis.
 5. The process inaccordance with claim 1, including adjusting a distribution of thepost-combustion gases to the individual post-combustion planes so thatlocal overheating of a surface of the charge material to greater than90% of the melting point of iron oxide that forms an oxidation layer isavoided, and so that a degree of post combustion at an upper outlet fromthe melting vessel is approximately 100%.
 6. The process in accordancewith claim 1, wherein the process gases, which comprise not only exhaustgases formed in the melting vessel, but also exhaust gases that areformed during the adjustment of the steel grade in the treatment vesseland flow into the lower part of the melting vessel through a connectionof gas spaces of the vessel, preheat the charge materials and arepost-combusted in stages as the process gases ascend in the meltingvessel.
 7. The process in accordance with claim 1, including supplyingenergy necessary for treating the melt in the treatment vessel at leastpartly by fossil fuels.
 8. The process in accordance with claim 1,including preheating the post-combustion gases and/or the gasesnecessary for melting the charge materials.
 9. The process in accordancewith claim 1, including removing at least a portion of the process gasesto be post-combusted and then post-combusting the process gases outsidethe column of charge material, and then returning the post-combustedgases to the column of charge material in a higher plane than the planefrom which the gases were removed.
 10. The process in accordance withclaim 9, including conveying the process gases to be post-combusted intopost-combustion spaces arranged along the wall of the melting vessel oroutside the melting vessel and/or in the wall of the interior shaft orinside the interior shaft, and introducing the post-combustion gasesinto the post-combustion spaces.
 11. The process in accordance withclaim 10, including systematically introducing the post-combustion gasesinto the post-combustion spaces with an injector effect.
 12. The processin accordance with claim 1, including carrying out combustion of thefossil fuels to melt the charge materials with less than astoichiometric amount of oxygen.